Preheat the oven to 425 degrees. Prepare a 12 muffin pan by lining with muffin wrappers. Lightly grease each muffin cup and set aside.
In medium sized bowl, mix together your dry ingredients: flour, baking powder, baking soda, cinnamon, and salt.
In a large bowl, beat together the butter and sugars until creamed. Now whisk in the eggs, vanilla extract, yogurt or sour cream, and milk. Whisk until smooth and combined.
Pour the dry ingredients into wet and continue to mix using a wooden spoon or rubber spatula. Now fold in the apples.
Spoon the mixture into each of the prepared muffin cups. Fill all the way to the top!
In a small bowl, make your crumb topping ingredients. Stir together the melted butter, brown sugar, cinnamon, salt, and oats. Spoon the mixture on top of each muffin cup.
Transfer to the oven and bake for 5 minutes at 425 degrees. Lower the temperature to 375 and bake another 15 minutes. Remove from oven and let cool for 5-10 minutes. You can enjoy warm right here, or transfer to a wired rack and let cool completely. Store in an air tight container. My preferred method is freezing shortly after baking!